The past decade has witnessed a great surge in research directed toward the development of inorganic materials operable in the fabrication of electronic circuit boards and integrated circuit packaging. For example, glass-ceramic coatings have been devised for application to metal substrates leading to the production of electronic circuit boards, and glass-ceramic substrates for use in integrated circuit packaging have been formulated. A specific goal of the latter compositions has been to replace alumina, the material conventionally used in that application.
The following three patents are illustrative of glass-ceramic coatings for application to metals:
U.S. Pat. No. 4,256,796 discloses compositions consisting essentially, in weight percent, of 16-50% BaO, 16-42% MgO, 12-34% B.sub.2 O.sub.3, and 10-23% SiO.sub.2. CaO, ZnO, ZrO.sub.2, Al.sub.2 O.sub.3, and SnO.sub.2 are noted as optional components.
U.S. Pat. No. 4,358,541 reports compositions consisting essentially, in weight percent, of 5-35% MgO, 0-35% CaO, 0-25% ZnO, 10-35% CaO+ZnO, 0-25% B.sub.2 O.sub.3, 0-10% P.sub.2 O.sub.5, 4-25% B.sub.2 O.sub.3 +P.sub.2 O.sub.5, and 25-50% SiO.sub.2. Al.sub.2 O.sub.3 in an amount up to 10% may be included as an optional ingredient. Where CaO is present in substantial amounts, the predominant crystal phases developed are diopside (CaO.MgO.2SiO.sub.2) and akermanite (2CaO.MgO.2SiO.sub.2). Where CaO is absent, the predominant crystal phases present are magnesium borate, willemite (2ZnO.SiO.sub.2), and enstatite (MgO.SiO.sub.2).
U.S. Pat. No. 4,385,127 describes compositions consisting essentially, in weight percent, of 10-60% BaO, 10-35% MgO, 5-30% B.sub.2 O.sub.3, 25-40% SiO.sub.2, and 5-20% CaO+ZnO+Al.sub.2 O.sub.3, consisting of 0-15% CaO, 0-16% ZnO, and 0-15% Al.sub.2 O.sub.3.
The following four patents are illustrative of glass-ceramic compositions utilized in substrates for integrated circuit packaging:
U.S. Pat. No. 4,221,047 provides two specific compositions, in weight percent, designed for that application.
______________________________________ SiO.sub.2 55.00 SiO.sub.2 52.5 Al.sub.2 O.sub.3 20.56 Al.sub.2 O.sub.3 21.0 MgO 20.00 MgO 21.5 AlPO.sub.4 3.44 P.sub.2 O.sub.5 2.0 B.sub.2 O.sub.3 1.00 B.sub.2 O.sub.3 1.0 ______________________________________
Cordierite (2MgO.2Al.sub.2 O.sub.3.5SiO.sub.2) constituted the predominant crystal phase.
U.S. Pat. No. 4,234,367 also discloses compositions, in weight percent, yielding glass-ceramics having cordierite as the predominant crystal phase.
______________________________________ SiO.sub.2 50.6-52.5 SnO.sub.2 0-2 Al.sub.2 O.sub.3 21-22 P.sub.2 O.sub.5 0-2 MgO 22-24.2 ZrO.sub.2 0-2 B.sub.2 O.sub.3 0.5-2 ______________________________________
U.S. Pat. No. 4,301,324 defines a range of glass-ceramic bodies wherein cordierite comprises the predominant crystal phase, but which also contain clinoenstatite and a secondary phase. Those compositions consisted essentially, in weight percent, of:
______________________________________ SiO.sub.2 48-55 P.sub.2 O.sub.5 0-3 Al.sub.2 O.sub.3 18-23 TiO.sub.2 0-2.5 MgO 18-25 SnO.sub.2 0-2.5 ZnO 0-2 ZrO.sub.2 0-2.5 Li.sub.2 O 0-1 TiO.sub.2 + SnO.sub.2 + ZrO.sub.2 .ltoreq.5 B.sub.2 O.sub.3 0-3 ______________________________________
U.S. Pat. No. 4,714,687 describes glass-ceramic materials containing willemite (2ZnO.SiO.sub.2) as the predominant crystal phase and cordierite as a secondary crystal phase. Those materials consisted essentially, in weight percent, of 15-45% ZnO, 3-15% MgO, 10-30% Al.sub.2 O.sub.3, and 30-55% SiO.sub.2.
Finally, U.S. application Ser. No. 42,980, filed Apr. 27, 1987 by L. M. Holleran, J. F. MacDowell and F. W. Martin under the title GLASS-CERAMICS FOR ELECTRONIC PACKAGING, records glass-ceramic materials containing cordierite as essentially the sole crystal phase which consist essentially, in weight percent, of 10-25% MgO+ZnO, consisting of 2-18% MgO+0-21% ZnO, 20-38% Al.sub.2 O.sub.3, 40-52% SiO.sub.2, and 2-15% total of at least one oxide in the indicated proportion of up to 8% total of K.sub.2 O, Rb.sub.2 O, and/or Cs.sub.2 O, up to 10% total of CaO, SrO, BaO, and/or PbO, and up to 5% B.sub.2 O.sub.3.
As was noted above, one specific goal underlying the research in glass-ceramic compositions for use in integrated circuit packaging has been to replace alumina in that application. A second objective has been to prepare materials demonstrating a coefficient of thermal expansion closely matching that of Al.sub.2 O.sub.3 (.apprxeq.65-10.sup.-7 /.degree.C. over the range 0.degree.-300.degree. C.) for use in such applications as leadless chip carriers. Therefore, the research has been directed to compositions exhibiting the five following characteristics;
(a) compatibility with copper, silver, and gold metallization;
(b) the capability of being co-fired at temperatures below 1000.degree. C. and, desirably, as low as 850.degree. C.;
(c) a dielectric constant less than that of Al.sub.2 O.sub.3 (.apprxeq.9-10 at ambient temperature);
(d) a smooth, flat surface without additional grinding and/or polishing; and
(e) a linear coefficient of thermal expansion (25.degree.-800.degree. C.) that can be carefully controlled over the interval of about 50-90.times.10.sup.-7 /.degree.C.